This invention relates to a flow rate transducer, more specifically to a tangential flow-in, vane type flow rate transducer for optically electrically measuring the flow rate of fuel, such as fuel supplied to the internal combustion engine of an automobile.
A prior art flow rate transducer of this type is so constructed that a vane wheel in a housing is rotated by a fluid tangentially introduced through a fluid inlet into a cylindrical fluid chamber in the housing and circulating the fluid in the fluid chamber, shielding plates are formed on the vane wheel at right angles to the plane of rotation thereof and arranged circumferentially at regular intervals, and a light emitting element and a light receiving element face each other with the locus of rotation of the shielding plates between them.
When the vane wheel is rotated by the circulation of the fluid in the fluid chamber, the shielding plates also rotate to intercept light beams emitted from the light emitting element toward the light receiving element. The rate of the light beam interception is converted into electric signals by a transducer circuit to determine the rotating speed of the vane wheel. Thus, the flow rate of the fluid which is substantially proportional to the rotating speed of the vane wheel would be obtained from said rotating speed and is displayed.
It has been known, however, that the flow rate transducer of this type is liable to cause errors between the actual values of flow rate and measured values, as shown by curve D in FIG. 6. The errors tend always to appear as large negative values in a low flow rate region and as large positive values in a high flow rate region.
Such large errors between the measured values and actual values would lower the reliability of the flow rate transducer. It is therefore essential to improve the flow rate measuring characteristic of the flow rate transducer.